Of course it is possible. How else are so many kids abducted? The cops screwed up in a huge manner.
Maybe people thought the guys taking her out were law enforcement and she was an arrest. No reason to get involved.
Moral: do NOT let your kids (male or female) go to the restroom alone...anywhere.
Adding: or friends, either. Always go in a group of at least three. Malls, theaters, sporting events, are all danger zones.
Little children should not go to the restroom alone. However, at age 15 , you should know better to not to run off with someone at a restroom. If you have a teenager with behavior issues, it will be tough to monitor them at all times.
This girl may have had history of being a runaway, maybe drug issues, and thats why the police did not intervene.